Graeme Souness has admitted mischief-making was a key factor when he shocked Scotland by signing Mo Johnston for Rangers.

It is 20 years since Souness stunned fans by taking on Rangers' first Catholic player in modern times and the memory still makes him smile.

In an exclusive interview, he said: "There was an element of mischief. I believed we were hurting Celtic by signing him.

"Stealing him from under their noses was a real smack in the chops for Celtic.

"They were our biggest rival and that's the name of the game."

At a Press conference at Ibrox, on July 10, 1989, Souness tried to lay to rest the bigotry that had haunted Rangers for 116 years.

He knew that to be taken seriously as a European team, Rangers couldn't continue the practice of not signing Catholics. And Souness didn't choose just any Catholic, he chose Celtic's poster boy, the striker who made the sign of the cross when he was sent off in the League Cup final against Rangers in 1986.

When Souness spotted Johnston in a newspaper posing in a Celtic shirt with the club's manager Billy McNeill, the seed was sown.

He said: "I had no idea Maurice was thinking of coming back until I saw that.

"It wasn't just signing a Catholic, it was signing a Catholic who had played for Celtic. It was a double whammy."

The prodigal son was coming back to Glasgow after a stint with French side Nantes and Celtic fans were ecstatic - but Souness had other ideas. He got his chance for devilment when he bumped into Johnston's agent Bill McMurdo at Ibrox.

Souness said: "I came down the stairs after a game at Ibrox and Bill McMurdo was leaning against a radiator.

"I said, 'You should have told me Maurice was thinking of coming back'. It was a throwaway line. I turned to walk away and he said 'Why? Would you be interested?'.

"I stopped in my tracks and turned back to talk to him."

McMurdo was a Rangers fan and he knew the money would be big. After all, Souness was on one of the biggest spending sprees British football had ever seen.

His predecessors had said they would sign a Catholic if the chance arose.

But Souness said: "Every manager politically would say yes but I actually meant it. I was married to a Catholic, my children were christened Catholics.

"I was brought up in Edinburgh. Every day I walked with a Catholic friend to school. It was never an issue in our house. I was brought up by very level-headed, right-thinking parents.

"Maybe I was naive but religion just wasn't an issue to me."

In his first three years at Rangers, Souness spent £11million and for the first time Rangers were attracting the best players available.

English clubs had been banned from Europe after the Heysel disaster and Hillsborough had led to the financially draining refurbishment of their stadiums. The money and the draw for the top players was no longer in the south and Souness considered the £1.5million needed to secure Johnston a"bargain".

One of the first to be told of the idea was Walter Smith, his assistant manager.

Souness said: "It took the wind out of his sails. He was stuck for words but after about a minute, he was fine and he thought it was a great idea."

He then drove to Edinburgh to see chairman David Murray.

Souness said: "At first, he just went silent but again within a minute thought it was a great idea.

"They both knew that if Rangers was to be accepted as a proper football club it couldn't have this ridiculous situation hanging over it."

Travelling in secret, separately from McMurdo, Souness flew to Paris and met Johnston in a suburban cafe. Souness said: "I persuaded him to sign for Rangers. I had played for Scotland with him. I had a relationship with him. It was relaxed and there were no difficult moments. It was an exciting time in Glasgow and he wanted to be part of it.

"He was a Scottish international, we needed a striker and he would complement what we had at the club."

The deal was kept secret for weeks but a month before it was publicly announced, Johnston confided in Rangers striker Ally McCoist when they shared a hotel room before Scotland played England.

McCoist said: "I was sworn to secrecy. I just could not believe it.

"I was more nervous than he was. I remember laughing nervously when he told me. He was fine about it. He just carried it off perfectly."

McCoist knew Johnston could help take Rangers to the top. He said: "I remember thinking that's a great player we are getting. I think Mo did it for football reasons.

"Graeme transformed Scottish football and wee Mo wanted to be part of that, to be part of the European scene and part of a team that was going to win."

McCoist remembers biting his lip when an irritated Souness dropped a hint of what was to come after Celtic secured the Scottish Cup.

"They've got a shock coming," announced a raging Souness to the dressing room but would say no more.

Celtic had already paid a deposit of £400,000 to Nantes for Johnston.

McNeill wanted to keep Johnston out of Rangers' clutches but his board refused to back him.

Souness said: "I have never spoken to Billy about it but he wouldn't have been best pleased."

Minutes after the Press conference announcing Johnston's arrival, Souness was faced with a thuggish gang of hate-filled Rangers fans who spat at his car and hurled abuse.

Some fans burned their season tickets and their scarves and death threats reached Ibrox.

But when he scored on his second outing, against Celtic, the doubters and some of the bigots were silenced.

Souness said: "I know there will still be people who think it shouldn't have been done but I am not interested in them. I wouldn't want to mix with people like that."

But he reserves his greatest praise for Johnston.

He said: "If anyone deserves credit, he does. He broke that ridiculous situation that existed here in Glasgow.

"Any level-headed person who has an interest in this country would think he has done his bit for Scotland."

What are your memories of the transfer? And did it really change the game in Scotland? Have your say below